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Circulation
Chapter 37 Part 2
37.7 Pressure, Transport,
and Flow Distribution
 Contracting ventricles put pressure on the blood,
forcing it through a series of vessels
•
•
•
•
•
Arteries carry blood from ventricles to arterioles
Arterioles control blood distribution to capillaries
Capillaries exchange substances
Venules collect blood from capillaries
Veins deliver blood back to heart
Human Blood Vessels
Fig. 37-17a, p. 648
outer
coat
smooth
muscle
basement
membrane
endothelium
Artery
elastic tissue
elastic tissue
Fig. 37-17a, p. 648
Fig. 37-17b, p. 648
outer
coat
smooth muscle rings basement
over elastic tissue
membrane endothelium
Arteriole
Fig. 37-17b, p. 648
Fig. 37-17c, p. 648
basement
membrane
endothelium
Capillary
(venules have a
similar structure)
Fig. 37-17c, p. 648
Fig. 37-17d, p. 648
outer
coat
smooth muscle,
elastic fibers
basement
membrane
endothelium
Vein
valve
Fig. 37-17d, p. 648
Blood Pressure
 Blood pressure
• The pressure exerted by blood on the walls of
blood vessels
• Highest in arteries, then declines through circuit
• Rate of blood flow depends on the difference in
blood pressure between two points, and
resistance to flow
Blood Pressure in the Systolic Circuit
arteries
capillaries
arterioles
veins
venules
Fig. 37-18, p. 648
Blood Flow
 Thick, elastic arteries smooth out variations in
blood pressure during the cardiac cycle
 Arterioles respond to signals from the autonomic
and nervous systems, and to chemical signals,
to direct blood flow to different parts of the body
Distribution of Cardiac Output
in a Resting Person
100%
lungs
heart’s right half
liver
digestive tract
kidneys
skeletal muscle
brain
skin
bone
cardiac muscle
all other regions
heart’s left half
6%
21%
20%
15%
13%
9%
5%
3%
8%
Fig. 37-19, p. 649
Controlling Blood Pressure
 Blood pressure depends on total blood volume,
how much blood the ventricles pump (cardiac
output), and whether arterioles are constricted or
dilated
 Receptors in the aorta and carotid arteries
monitor blood pressure and send signals to the
medulla, which regulates cardiac output and
arteriole diameter
Measuring Blood Pressure
Animation: Measuring blood pressure
37.8 Diffusion at Capillaries,
Then Back to the Heart
 Capillary
• A cylinder of endothelial cells, one cell thick
• Capillary beds are diffusion zones, where blood
exchanges substances with interstitial fluid
• Hydrostatic pressure moves materials out
(ultrafiltration)
• Osmotic pressure moves water in (capillary
reabsorption)
Fluid Movement at a Capillary Bed
blood to
venule
high pressure
causes outward flow
blood from
arteriole
cells of
tissue
inward-directed
osmotic movement
B
A
Fig. 37-21 (a-b), p. 650
Venous Pressure
 Venules deliver blood from capillaries to veins
 Veins deliver blood to the heart
• Large-diameter, blood volume reservoirs
• Valves help prevent backflow
• Amount of blood in veins varies with activity level
Venous Valve Action
Fig. 37-22a, p. 651
venous valve
Fig. 37-22a, p. 651
Fig. 37-22b, p. 651
blood flow to heart
valve
open
valve
closed
Fig. 37-22b, p. 651
Fig. 37-22c, p. 651
valve
closed
valve
closed
Fig. 37-22c, p. 651
37.7-37.8 Key Concepts
Blood Vessel Structure and Function
 The heart pumps blood rhythmically, on its own
 Adjustments at arterioles regulate how blood
volume is distributed among tissues
 Exchange of gases, wastes, and nutrients
between the blood and tissues takes place at
capillaries
37.9 Blood and Cardiovascular Disorders
 Red blood cell disorders
• Anemias, beta-thalassemias, polycythemia
 White blood cell disorders
• Infectious mononucleosis, leukemias, lymphomas
 Clotting disorders
• Hemophilia, thrombus, embolus
Blood and Cardiovascular Disorders
 Atherosclerosis
• Buildup of lipids in the arterial wall that narrows
the lumen, may rupture and trigger heart attack
Fig. 37-23a, p. 652
wall of artery,
cross-section
unobstructed
lumen of
a normal
artery
Fig. 37-23a, p. 652
Fig. 37-23b, p. 652
atherosclerotic
plaque
blood clot
sticking to
plaque
narrowed
lumen
Fig. 37-23b, p. 652
Clogged Coronary Arteries
coronary
artery
Fig. 37-24a, p. 653
aorta
coronary
artery
blockage
location of a shunt
made of a section
taken from one of
the patient’s other
blood vessels
Fig. 37-24b, p. 653
Blood and Cardiovascular Disorders
 Hypertension – a silent killer
• Chronic blood pressure above 140/90
 High blood pressure and atherosclerosis
increase the risk of heart attack and stroke
Blood and Cardiovascular Disorders
 Arrhythmias –
abnormal heart
rhythms
• EKGs record
electrical activity of
cardiac cycle
one normal
heartbeat
0 0.2 0.4 0.6 0.8
a time (seconds)
bradycardia
(here, 46
beats per
minute)
b
tachycardia
(here, 136
beats per
minute)
c
ventricular
fibrillation
d
Fig. 37-25, p. 653
Risk Factors
 Cardiovascular disorders are the leading cause
of death in the United States
 Risk factors
• Tobacco smoking, family history, hypertension,
high cholesterol, diabetes mellitus, obesity, age,
physical inactivity, gender
37.9 Key Concepts
When the System Breaks Down
 Cardiovascular problems include clogged blood
vessels or abnormal heart rhythms
 Some problems have a genetic basis; most are
related to age or life-style
37.10 Interactions With
the Lymphatic System
 Vessels and organs of the lymphatic system
interact closely with the circulatory system
 Lymph vascular system
• Lymph capillaries and vessels that collect water
and solutes from interstitial fluid and deliver them
to the circulatory system
Three Functions of
the Lymph Vascular System
 Returns fluids and plasma proteins that leak out
of capillaries to the circulatory system
 Delivers fats absorbed from the small intestine to
the blood
 Transports cellular debris, pathogens, and
foreign cells to lymph nodes
Lymphoid Organs and Tissues
 Lymph nodes
• Organs that filter lymph before it enters blood and
identify pathogens
 Tonsils in throat and adenoids in nasal cavity
• Respond to inhaled pathogens
Lymphoid Organs and Tissues
 Spleen
• Filters pathogens and worn out blood cells from
blood
 Thymus gland
• Matures T lymphocytes essential to the immune
system
Components of the Lymphatic System
Fig. 37-26a, p. 654
Tonsils
Defense against bacteria and
other foreign agents
Right Lymphatic Duct
Drains right upper portion of the body
Thymus Gland
Site where certain white blood cells
acquire means to chemically
recognize specific foreign invaders
Thoracic Duct
Drains most of the body
Spleen
Major site of antibody production;
disposal site for old red blood cells
and foreign debris; site of red blood
cell formation in the embryo
Some Lymph Vessels
Return excess interstitial fluid and
reclaimable solutes to the blood
Some Lymph Nodes
Filter bacteria and many other
agents of disease from lymph
Bone Marrow
Marrow in some bones is
production site for infectionfighting blood cells (as well as
red blood cells and platelets)
Fig. 37-26a, p. 654
Fig. 37-26b, p. 654
lymph
capillary
interstitial
fluid
flaplike
“valve”
made of
overlapping
cells at tip of
lymph
capillary
capillary bed
Fig. 37-26b, p. 654
Fig. 37-26c, p. 654
lymph trickles past organized
arrays of lymphocytes
valve (prevents backflow)
Fig. 37-26c, p. 654
Animation: Human lymphatic system
Animation: Lymph vascular system
37.10 Key Concepts
Links With the Lymphatic System
 A lymph vascular system delivers excess fluid
that collects in tissues to the blood
 Lymphoid organs cleanse blood of infectious
agents and cellular debris
Animation: Capillary forces
Animation: Examples of ECGs
Animation: Vein function
Animation: Vessel anatomy
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